Is there a blood test for Alzheimer's? Yes there is, but it's not yet available in doctors' offices.

Jessica Hall

The study found that blood tests were more accurate than those seen by GPs or specialists.

A blood test is more successful than a doctor at determining whether someone has memory loss due to Alzheimer's disease, according to a new study, but more research is needed to figure out how to best apply the technology.

The Alzheimer's blood test used in the study was 91% accurate. In comparison, evaluations by neurologists and other memory specialists were accurate at diagnosing Alzheimer's 73% of the time, while evaluations by primary care providers were only 61% accurate, the study found.

The study, published Sunday in JAMA, followed 1,213 people with an average age of 74.2 years who underwent cognitive testing at general practices and specialty clinics in Sweden, and the data was presented at this year's Alzheimer's Association International Conference in Philadelphia.

Read: For Alzheimer's patients, study finds this Novo Nordisk GLP-1 drug slows cognitive decline

Brain changes can begin years, or even decades, before symptoms appear, so early detection could help people make lifestyle changes in terms of medication and diet, but more research is needed before people can get a blood test at their local clinic.

“Accurate blood tests for Alzheimer's disease (AD) may streamline the diagnosis and treatment of AD,” the researchers wrote in the study. “Future studies are needed to evaluate how the use of blood tests for these biomarkers could impact clinical care.”

Alzheimer's is difficult to diagnose. Studies show that specialists misdiagnose symptoms of the disease in at least a quarter of patients, and general practitioners probably misdiagnose even more.

About 6.9 million Americans have Alzheimer's disease, according to the Alzheimer's Association. The risk of developing dementia doubles every five years after age 65, and by age 85, roughly one in three Americans will have dementia, most of whom are women, the Alzheimer's Association says.

As the population ages, demand for medicines to treat and prevent Alzheimer's and other dementias is growing. The global market for Alzheimer's drugs is expected to grow from $4.82 billion in 2023 to more than $8.18 billion by 2032, according to research from consulting firm Towards Healthcare.

The blood test that shows the most promise for identifying brain changes linked to Alzheimer's assesses the phosphorylated tau (p-tau) protein, a biomarker for Alzheimer's that can build up before patients show signs of cognitive impairment.

A specific marker, p-tau217, increases over time correlate with worsening cognitive function and brain atrophy. p-tau217 testing also predicts the likelihood of amyloid plaques in the brain, another biomarker for Alzheimer's disease and the target of recently approved treatments.

“The blood test shows the potential to improve and potentially redefine the recruitment process and diagnostic workup for Alzheimer's clinical trials if (a) it is more than 90% accurate in large populations and (b) it becomes more widely available,” Maria Carillo, chief scientific officer and medical affairs officer at the Alzheimer's Association, said in a statement.

“Currently, primary and secondary care physicians must use a combination of cognitive testing and blood or other biomarker tests to diagnose Alzheimer's, but a blood test could improve the accuracy of early diagnosis and maximise the chances of receiving Alzheimer's treatment as early as possible for better outcomes,” Carillo said.

Tests that are sometimes only available in specialized clinics, such as positron emission tomography, known as PET, and sampling of cerebrospinal fluid to evaluate biomarkers of Alzheimer's disease, reduce the rate of misdiagnosis.

Other conditions, such as depression, thyroid disease, sleep apnea, and vitamin B12 deficiency, can also affect cognitive function, so a definitive diagnosis of Alzheimer's is often made after an autopsy, and other tests, such as spinal taps and PET scans, are expensive, invasive, and not always available, according to the Alzheimer's Association.

Some of the newest dementia drugs, such as lecanemab and donanemab, require positive results from Alzheimer's biomarker tests. But general practitioners often rely on paper-and-pencil tests to diagnose Alzheimer's, rather than biomarker tests. Specialists can have long wait times and limited access to PET scans and spinal taps, the JAMA researchers say.

“The lack of accessible methods to test for Alzheimer's disease biomarkers represents a major obstacle to the initiation and effective use of anti-amyloid immunotherapy in the treatment of patients with Alzheimer's disease,” the study added.

Lead study author Oscar Hansson from Lund University called the research “a major step towards the global clinical implementation of a blood test for Alzheimer's disease.”

“This highlights the need for Alzheimer's biomarkers to help make more accurate diagnoses,” said Hanson. “The next step is to establish clear guidelines for how Alzheimer's blood tests can be used in clinical practice, hopefully implementing these tests first in specialty care and then in primary care. This work is currently underway.”

-Jessica Hall

This content was produced by MarketWatch, an operation of Dow Jones & Co. MarketWatch is published independently of Dow Jones Newswires and The Wall Street Journal.

(End) Dow Jones Newswires

08-03-24 1712ET

Copyright (c) 2024 Dow Jones & Company, Inc.